·        0.9% of outpatient doctor-visits reported by sentinel physicians during week 17 were attributed to ILI, down from 1% reported during week 16 and below baseline (2.4%). Pennsylvania Department of Health works with a network of 145 sentinel physicians across the state (pediatricians, family medicine and colleges) to track the proportion of flu-like illness seen in outpatient settings weekly. Sentinel providers have an agreement with the state lab to submit samples year-round, and the state uses test results from these submissions to monitor influenza viruses that are circulating in the commonwealth throughout the year. Providers may join the sentinel network by contact Dr. Owen Simwale at owsimwale@pa.gov.  

·       147 flu cases were reported during week 17, down from 308 cases (adjusted for late reporting) reported during week 16. Influenza cases continue to be reported in all age groups and regions of the state. Altogether, 44,308 lab positive cases have been reported season-to-date. 

·    Influenza viruses were detected in 7% of respiratory samples that were submitted to the state lab for confirmatory testing during week 17, down from 10% positivity reported during week 16. The positivity of respiratory samples is a proxy for disease prevalence - an estimate of how much of the flu-like illnesses we are seeing is actually caused by flu viruses. Because influenza was only detected in less than a tenth (<10%) of all persons presenting with ILI, for whom respiratory specimens were submitted to the state lab last week, other respiratory viruses should be considered as possible causes of influenza in persons presenting with flu-like symptoms. It should also be noted that as the prevalence of influenza goes down, rapid diagnostic test kits do not perform as well. Therefore, more accurate tests, including rt-PCR and culture, should now be used for influenza diagnostic testing.

                    * The Pennsylvania Department of Health is closely following the outbreak on avian H7N9 in China. At this time, no human infections with this virus have been detected in the United States. PADOH has enhanced surveillance for influenza in persons returning from China, to make sure that any 'imported infection with H7N9" is promptly detected and controlled. The most current CDC guidance on H7N9 is posted at, http://www.cdc.gov/flu/avianflu/h7n9-virus.htm.*

·    Other respiratory viruses that are co-circulating with influenza at this time include, respiratory synctial virus (RSV), rhinovirus, adenovirus, parainfluenza viruses and coronavirus. Coronavirues are known to cause a majority of common colds in humans. Further information on coronaviruses, including differences between flu and these viruses, can be found at http://www.cdc.gov/coronavirus/about/index.html.

·    A majority (>90%) of circulating flu viruses, at this time, continue to be influenza type B. It is typical to see an increase in influenza type B viruses after peak season, as the season winds down. Influenza type B viruses generally cause milder illness than type A viruses, but can still result in serious complications. A majority (80%) of circulating influenza type B viruses are covered by the current vaccine and recent vaccine effectiveness data shows that the current vaccine gives much better protection against flu type B viruses than type A viruses (70% vs. 47%).

·        A majority (>90%) of circulating influenza type A viruses continue to be the A/H3N2 subtype, a strain that generally causes severe illness in older age groups. A majority (99%) of circulating viruses (A/H3/N2, H1N1 and flu type B) are similar to strains included in this year's influenza vaccine. Even though recent data shows that the elderly did not mount effective immunity from the vaccine, vaccination remains the best protection we have against influenza. Influenza vaccination prevents up to 50% influenza illness in persons under 65 years of age which in turn reduces the likelihood of transmission to older persons. Further, vaccination is known to reduce the duration and severity of illness - if a vaccinated person gets the flu. Because there is still a lot of flu activity and the season is not over, it is still not too late to get vaccinated against influenza.

·       The state lab can now monitor influenza viruses for sensitivity to antiviral medications. Nearly all viruses tested so far are sensitive to current antiviral medications. During week 7, the state lab detected an influenza A/H1N1 virus which was resistant to Tamiflu. No additional viruses of this nature have been detected in Pennsylvania; suggesting that nearly all circulating A/H1N1 viruses remain sensitive to Tamiflu.

·        17 flu-related hospitalizations were reported during week 17, down from 21 hospitalizations reported during week 16. Altogether, 3,686 hospitalizations have been reported season-to-date. The median age of hospitalizations is 80 years (range 0 to 99) years. While the overall number of hospitalizations has plateaued, the proportion of elderly among those hospitalized has increased. The elderly currently account for 22% of all reported cases but nearly 70% of all reported hospitalizations.

·      Altogether, 490 outbreaks of influenza in long term care facilities have been reported this season.  A majority of these outbreaks have since resolved; but they involved over 3000 illnesses, more than 100 hospitalizations and about 150 deaths among Pennsylvania seniors. This is further evidence of the impact influenza can have on the elderly. Vaccinating employees and residents of long term care facilities, along with infection control practices, can limit the impact of influenza. A list of Pennsylvania hospitals and long term care facilities with >90% influenza vaccine coverage among employees can be found at, http://www.portal.state.pa.us/portal/server.pt?open=514&objID=1008994&mode=2.